This invention relates, in general, to optical signal processors and, more specifically, to acousto-optic processors for space-integrating vector-matrix multiplication by inner product techniques.
Processing of data containing a large number of separate values is required in several applications, such as in synthetic aperture radar systems and in spectrum analyzers. The quantity of data to be mathematically manipulated often represents a difficult task for even high-speed conventional digital processing techniques, including general and special purpose digital computers.
In many cases, the data is available in matrix and/or vector form, and typically these data expressions must be multiplied together to obtain a resulting matrix or vector of values. In order to accomplish these tasks as quickly as possible, optical processing techniques have been developed. While many optical systems yield high-speed number processing, they are analog devices and fail to give the accuracy desired and obtainable by slower non-optical digital processors.
To overcome these problems, efforts have been made to provide processing techniques which give the speed of optical systems along with the accuracy and precision of digital systems. Accuracy better than the 7 to 9 bit accuracy of conventional optical analog systems is desirable. Such improvement is claimed by processes which implement digital multiplication using analog convolution and which uses two's complement arithmetic. An implementation of the former has been suggested in connection with an acousto-optic systolic system for rapid and accurate vector-matrix multiplication wherein optics is used for the parallel formation of the M element products and wherein M detectors are required for their detection, where M is the dimension of the input vector.
General background on optical processing is described in the article, "Optical Computing," contained in Computers and Electronics, January, 1985, pp. 64-67 and 82. A more technical description of optical processing is contained in "Bragg Signal Processing and Output Devices," published by the International Society for Optical Engineering, in 1982.
A prior art system described by William T. Rhodes in "Acousto-Optic Signal Processing: Convolution and Correlation," Proceedings of the IEEE, Volume 69, No. 1, June, 1981, uses spatial light modulators for signal processing. In the single cell systems desribed therein, reference masks, which may be phototransparencies, are used as a means for changing the light passing through the acousto-optic cell. The two-cell systems described by Rhodes are significantly different from the teachings of the present invention.
U.S. Pat. No. 4,389,093, issued on June 21, 1983, teaches a method and apparatus for coherent detection in optical processors. While this patent teaches the use of a spatial light modulator followed by a spherical lens and a photodetector, it does not use a second spatial light modulator as does the present invention, but uses an optical mask. Other significant features distinguish the present invention from the device taught in the referenced patent.
It is desirable, and it is an object of this invention, to provide an optical processor having fast computational speed, high bit accuracy, and a simple hardware configuration.